In recent years, the Universal Serial Bus (USB) has become one of the most widely used methods for interconnecting electronic devices. The USB standard is, e.g., available from www.usb.org. Originally USB was used to interconnect computers to various standard peripheral devices. However, deployment of the USB standard has grown to support a vast array of devices and in particularly portable devices such as e.g. cellular phones, personal digital assistants (PDAs), cameras and personal music players etc.
Logically, the USB standard provides a system with an inverted tree-like structure. The top of the tree (i.e., at the root since the tree is inverted) comprises the USB host to which a plurality of USB devices can be connected. If more USB devices are required, a USB hub may be used. A USB hub may be further connected to its own set of USB devices or USB hubs as necessary. The USB connections between the USB host, the USB hubs and the USB devices allow data to flow between the USB host and USB devices.
Physically, the USB standard is based on a serial bus comprising a pair of twisted wires for communicating two data signals labeled D+ and D−. The USB standard also defines a single wire for providing a 5 V (volts) power signal labeled VBUS. Devices connected to a USB host or a USB hub are allowed to draw a limited amount of power from the VBUS. Therefore, the USB standard requires that each USB host and USB hub provide power for the USB devices connected thereto.
Initially, a USB device is only allowed to draw 100 mA from the VBUS power signal. However, it may request more current from the upstream USB host or USB hub in units of 100 mA up to a maximum of 500 mA. In practice, most ports will deliver the full 500 mA without any request before the port shuts down the power. Hence, if a USB device requires more power than the available 500 mA the device cannot operate until the user changes the network, either by rearranging USB connections or by adding external power resources. Typically, large USB devices, such as e.g. disk drives and printers, include their own power supplies and do not draw power from their USB connections. Smaller devices, on the other hand, may be partially or fully powered from their USB connections.
As already mentioned, the USB standard has become increasingly popular in connection with portable devices such as cell phones, personal digital assistants (PDAs), cameras and personal music players etc. Adding a USB port to a portable device makes it easy to upload and download information including names, phone numbers, calendars, photographs and music etc, which provides the possibility of increased portability.
Of particular interest in connection with the present invention is the possibility of utilizing a USB port and the VBUS power signal therein for charging the battery or similar power source in a portable device. This is especially convenient in connection with cell phones allowing the users to charge their cell phones at work, for example, without the use of specialized wall adapters. Among USB devices, chargers are somewhat anomalous since they use the USB connection for power and not for data transfer.
FIG. 1 shows a portable device in the form of a cell phone 10 comprising a display 22 and a key pad 12 as is well known in the art. The exemplifying cell phone 10 comprises a connector 14 arranged at its lower short end for connecting various peripheral devices, such as e.g. earphones, loudspeakers, chargers, photo flashes, external memory devices and even computers or similar. Almost every commercially available cell phone comprises a similar connector for connecting peripherals. In the given example the connector 14 is arranged as a so-called FastPort connector which is commonly used in many cell phones provided by the company Sony Ericsson. As can be seen in FIG. 1, the FastPort connector comprises twelve terminals 1-12.
FIG. 2a shows a table presenting the terminals 1-12 of the exemplifying FastPort connector 14 in FIG. 1. In this connection, terminals 1 and 9-12, which are singled out in FIG. 2a, are of special interest in connection with the present invention. Terminal 1 of the connector 14 is arranged to be connected to the above mentioned USB signal VBUS for receiving power from the USB host or USB hub as may be the case. Terminal 9 is arranged to be connected to the USB signal ground (GND), whereas terminal 10 and 11 are arranged to be connected to the USB data signals D+ and D− respectively for communicating data between the USB and the cell phone 10.
However, the charging terminal 12 (Charge in) has no explicit relation to the USB terminals 1, 9, 10 and 11 of the connector 14, since it is arranged to draw charging power from an external power source for charging the battery or similar power source of the cell phone 10, i.e. the charging terminal 12 is not a part of the USB and the USB standard.
Before we proceed it should again be emphasized that the FastPort connector 14 describe above is merely an example. Other portable devices and other cell phones in particular may have other connectors comprising terminals arranged to be connected to the USB signals VBUS, D−, D+ and GND respectively and a charging terminal being arranged to draw charging power from an external power source for charging a battery or similar power source in the portable device.
Even if a USB port can charge a USB device via the VBUS power signal as mentioned above, the VBUS signal cannot be safely connected to a charging terminal like the terminal 12 in the FastPort connector 14 of the cell phone 10. This is due to the fact that a charging port is generally adapted to draw the required amount of charging power from the charging source without considering the maximum 500 mA provided by the VBUS. Hence, the required charging power may very well exceed 500 mA causing the VBUS to perform poorly, shut down, or even be overloaded. In other words, a cell phone 10 or a similar portable device having a charging terminal adapted to draw power from an external power source cannot be safely connected to the USB VBUS, since the device may require a charging power that exceeds the power available from the VBUS causing the VBUS signal to shut down or malfunction or even cause the USB host or USB hub in question to be overloaded and possibly destroyed.
FIG. 2b shows a table of the signals for each terminal 1-4 in an ordinary USB connector. As can be seen, terminal 1 provides the USB signal VBUS, terminal 2 the USB signal D−, terminal 3 the USB signal D+ and terminal 4 the ground GND. There may be variations among the USB connectors. In case the numbering and layout etc varies the terminals 1-4 in a common USB connector as indicated in FIG. 2b applies mutatis mutandis. 
FIG. 3 is a schematic illustration of an exemplifying ordinary USB-cable 300a arranged to operatively connect the cell phone 10 in FIG. 1 to a USB port. At one end the USB-cable 300a comprises a USB-connector for connecting the cable 300a to a mating USB connector of a USB host or a USB hub as may be the case. At the other end the USB-cable 300a comprises a phone-connector for connecting the cable 300a to the FastPort connector 14 of the cell phone 10 as described above. It should be emphasized that other USB-cables may have other phone-connectors or similar device-connectors that are adapted to be connected to connectors of other cell phones or similar portable devices for enabling an USB connection between the device and a USB host or USB hub.
As can be seen in FIG. 3, in the USB-cable 300a the USB-connector terminal 1 (VBUS) is connected to the phone-connector terminal 1 (USB+5V), the USB-connector terminal 2 (D−) is connected to the phone-connector terminal 11 (USB DATA−), the USB-connector terminal 3 (D+) is connected to the phone-connector terminal 10 (USB DATA+), and USB-connector terminal 4 (GND) is connected to the phone-connector terminal 9 (GND).
The exemplifying ordinary USB-cable 300a in FIG. 3 is not intended for providing a charging power from an external charger. Thus, the USB-cable 300a is not providing a connection to the charging input on terminal 12 (Charge in) in the phone-connector of the USB-cable 300a. As explained above, it is not safe to provide a connection from e.g. the VBUS power signal to a charging input as the charging input at terminal 12 (Charge in). Rather, in case the cell phone 100 is to be charged by a an external charger this is accomplished via a dedicated charging-cable 300b, as will be described in more detail below with reference to FIG. 4.
FIG. 4 is a schematic illustration of an exemplifying combined USB-and-charging set-up. The set-up comprises a desk stand 300c, a dedicated charging-cable 300b and the USB-cable 300a as discussed above. The desk stand 300c enables the cell phone 10 to receive charging power via the charging-cable 300b at the same time as it may communicate with other USB devices via the USB-cable 300a. To this end the desk stand 300c comprises a first cable-connector for connecting the phone-connector of the USB-cable 300a and a second cable-connector for connecting the phone-connector of the charging-cable 300b. The phone-connector of the charging-cable 300b and the phone-connector of the USB-cable 300a are preferably of the same type and both phone-connectors are preferably adapted to mate with the FastPort connector 14 of the cell phone 10 as described above with reference to FIGS. 1 and 2a. As is evident form FIG. 4, the phone-connector of the charging-cable 300b is arranged to connect to terminal 9 in the connector 14 for supplying ground (GND) from a charger to the cell phone 10, and arranged to connect to terminal 12 in the in the connector 14 for supplying a charging power from a charger to the cell phone 10.
Desk stands of the kind now described are commercially available (see e.g. the desk-stand CDS-60 from Sony Ericsson) and well known to those skilled in the art and they need no further description. The desk stand 300c illustrates one solution in which a USB-cable 300a is combined with a charging-cable 300b. Naturally, as is well known, the USB-cable 300a and the charging-cable 300b can also be used separately one at the time by connecting the phone-connector of the cables 300a, 300b respectively to the connector 14 of the cell phone 10 or together mechanically stacked if a mechanical stacking is allowed.
As is clear from the known solutions described above, USB cables are typically not used for connecting an external charger to a charging terminal of a portable device, e.g. such as the charging terminal 12 in the connector 14 of the cell phone 10. However, some countries have decided that portable devices and particularly cell phones provided in their country should be arranged to be charged by a proposed external charger with a USB-interface that provides charging power on the USB signal VBUS and a short circuit between the USB data signals D+ and D− to allow identification of this type of charger.
FIG. 5a is a schematic illustration of the exemplifying ordinary USB-cable 300a as discussed above now being connected to the proposed external charger. In FIG. 5 the signals in the USB-connector of the USB-cable 300a have been schematically connected to the terminals of the external charger by means of dashed lines. In addition, as can be seen in FIG. 5a, the USB data signals D− and D+ are connected to each other in the external charger via a short circuit 520.
Even though the ordinary USB-cable 300a is not intended for connecting an external charger to a charging terminal, e.g. as terminal 12 in connector 14 of the cell phone 10, a simple solution for achieving a charging function via the USB-cable 300a would seemingly be to provide an extra connecting wire between terminal 1 (VBUS) of the USB connector and terminal 12 (Charge in) of the phone connector in USB-cable 300a. However, if a USB-cable modified in this way is accidentally used for connecting the cell phone 10 or similar portable device to an ordinary USB host or USB hub, the cell phone 10 or similar may draw an amount of power from its charging terminal 12 that exceeds the amount available from the VBUS of the USB host or USB hub. In that case the VBUS power signal may shut down or malfunction and the USB host or USB hub may even be overloaded and possibly destroyed. Hence, this is not a safe solution.
Another solution may be to adapt the cell phone 10 or similar portable device to only draw full charging power from the proposed external charger via the VBUS when the device senses the short circuit 520 in the proposed external charger. However, even if this may be a future solution many existing USB devices, such as older cell phones and other older portable devices, are not adapted to receive full charging power via the VBUS. Hence, this solution is not compatible backwards with older existing USB devices such as older cell phones and other portable USB devices. In addition, the necessary adaptation of the cell phone 10 or similar portable USB device requires additional circuitry and possibly additional software which is costly and which may malfunction.
Still another solution may be to provide a cable for the proposed external charger with intelligent circuitry being arranged to operatively sense the short circuit 520 in the proposed charger and temporarily connect terminal 1 (VBUS) of the USB connector to terminal 12 (Charge in) of the phone-connector in USB-cable 300a. However, this requires additional circuitry which is costly and which may malfunction.
In view of the above there seems to be a need for an improved external charging via an charging-cable with an USB like connector, which charging requires a minimum of extra circuitry and/or software and which guaranties none or minimum damages and/or malfunctions if the charging-cable is accidentally utilized in an ordinary USB connector.